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Old 08-18-2017, 06:50 PM
FrankieKat FrankieKat is offline
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Join Date: Feb 2012
Location: Brooklyn, NY, USA
Posts: 42
Quote:
Originally Posted by Electronic M View Post
If it had a brightener on it, it is that dim, and the CRT bias voltages and HV are in spec, then may as well put the brightener back on and see how decent of a pic it can make and for how long.

B&W CRTs prior to ~1960 were often not nearly as bright as newer CRTs we are used to seeing....That said it does look dim for a tube of it's era.

I may have a good spare 21ALP4. IIRC I sold one this spring, and I think I had 2 before then.

Since the vertical is rolling and the horizontal is stable I'd suggest checking the vert and sync separator tubes, checking all resistors in those stages and replacing any that are out of tolerance.
So with the contrast at about 10%, the CRT voltages are on spec, though there's no picture at all until contrast is past about 90%. The B+ supply voltages are right on too. I don't have a HV test probe though so can't measure the HV unfortunately. I've been checking resistors and only have had to replace two or three, and the worst was maybe 25% off so clearly they used good parts.

Have tried a few different vert, sync and AGC tubes and have the best ones in there now, though there wasn't a huge difference. Both horiz and vertical lock are fairly poor and only get solid horiz lock with the control is the extreme end. It also seems to get worse as the set heats up.

Nothing I've done has improved or changed the brightness. Put the brightener back on for a little bit but improvement was minimal if any. That video was recorded in a pitch black room and it actually seems a bit brighter on the video than in person.

I'm going to keep grinding and checking voltages and components and see what happens.

Thanks for the tips!

FK
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